I don't know why but for the life of me i can't remember or find what you use the gems for again, can any one enlighten me?

If you're talking about the etc., they're used to transform your pet to Galactic .

You need to use the gems to complete Iltallo's quest when the Coda Caves are open. They are open the 6th and 7th of every month.

How do you get Iltallo's quest?

He is located on Atebus, the moon of Subeta. :) (Explore link.)

I looked all over Atebus and can't find him. What part of Atebus is he in?

Coda Caves (click). He is only there when you can collect gems, I believe.

He is at the Coda Caves every 6th and 7th of each month.